(1) Field of the Invention
The invention relates to annular reactors such as those used in steam reforming for producing hydrogen from a hydrocarbon fuel.
(2) Description of the Prior Art
Catalytic reactors for converting hydrocarbon fuel to hydrogen are well known in the art. The reactors are of tubular design and may have an inner cylindrical wall with catalyst interposed between the walls. Vaporized hydrocarbon fuel mixed with steam is circulated through the catalyst to produce hydrogen. Typically, the reactors are about 2 to about 40 feet long and have diameters less than about one foot. The outer wall of the reactor is heated to provide energy for the endothermic conversion of hydrocarbon fuel to hydrogen. During the operation of such reactors, the reactors undergo temperature cycling during heat up to operating temperature and cool down when the reactor is not in service. The reactor walls and catalysts disposed within the reactor may be cycled through a temperature of as much as 2000.degree. F.
During thermal cycling, the catalyst tends to be crushed. During the part of the thermal cycle when the temperature of the reactor is being elevated, the walls of the reactor expand creating a positive change in the internal volume of the reactor. During the time that the reactor's temperature is being elevated, the catalyst disposed within the reactor also expands. However, since the coefficient of expansion of the walls of the reactor exceeds the coefficient of expansion of the catalyst, the internal volume of the reactor expands more than the volume of the catalyst creating voids within the catalyst. The voids are filled by catalyst which tends to slump downwardly into the voids.
Upon cool down, the walls of the reactor contract and there is a decrease in internal volume of the reactor. However, since catalyst has been redistributed downwardly within the reactor, due to slumping, cooling of the reactor results in compaction of the catalyst by mechanical pressure exerted by reactor walls against the catalyst. A portion of the pressure is absorbed by the partially elastic walls, and a portion is absorbed by the partially elastic catalyst material. However, it has been found that at excessive pressures, the catalyst is crushed and if the catalyst is particularly strong the outer walls of the reactor may deform beyond their elastic limit. As the reactor is cycled through many thermal cycles, the catalyst crushing problem becomes more severe after each thermal cycle. If enough catalyst is crushed, voids in the catalyst bed are reduced, increasing process pressure drop. The reactor may become clogged to a point where it is necessary to remove the crushed catalyst and insert new catalyst.
It is an object of the present invention to provide a reactor which reduces crushing of solid particles disposed within the walls of the reactor.
It is a further object of the present invention to reduce or eliminate reactor deformation and failure during repeated thermal cycling of the reactor.
It is another object of the present invention to extend the number of cycles a bed of catalyst can be used.